Take a moment to consider a system in which an inverter unit (i.e., power electronics device) that converts the power is provided with a communication function and autonomous cooperative control such as phase synchronization of output power and allocation of output/input power amount is applied between a plurality of power electronics devices to maintain the flexibility of operations while automatically implementing a capacity change even at the time of expansion and the time when an abnormality occurs.
It is necessary to provide a phase synchronization of output power function in, for example, an application in which a plurality of power electronics devices are driven in parallel to increase the output of power. The phase synchronization of output power function is to prevent an occurrence of cross current (e.g. reactive current caused by a difference of electromotive force, synchronization cross current caused by a phase difference of electromotive force and harmonic cross current caused by a waveform difference of electromotive force) in an output on the alternating-current side. Also, the allocation of output/input power amount function is to drive a plurality of power electronics devices in parallel and distribute the power efficiently for the load of a motor drive or the like.
In this case, it is useful for the throughput increase in the power input/output to determine the subject of control between the plurality of power electronics devices, that is, to determine a master (i.e. device of a control subject) and a slave (i.e., device of a controlled subject) and give an instruction of power information and synchronization information (e.g., time synchronization information and frequency information) from the master to the slave for phase synchronization of output power. In a case where three or more power electronics devices are connected to the same power line, since it is difficult only with information on the power line to recognize individual actual values with respect to the planned values of respective devices, power information is exchanged using the communication function and the master synchronizes with the slave.
In the related art, there is disclosed a method in which a plurality of inverters, to which the master/slave role is fixedly set, realize parallel running corresponding to phase synchronization of output power by the use of an optical communication line. Moreover, there is disclosed a method in which, by notifying device information to a server by the use of a communication function when a device connects to a system, software on the server that monitors and controls the device is automatically set.
However, in the case of automatically determining the master/slave role between a plurality of power electronics devices, since the devices individually operate at the time of initial installation or anomalous occurrence, if the defined state of a logical configuration that controls power is not considered, the operations may start in a state where there are a plurality of masters in the system. In this case, since it is difficult to unify a decision as to from which power electronics device the synchronization information is received for operation, there is a problem of an autonomous cooperation function such as phase synchronization of output power and allocation of output/input power amount unable to correctly operate. Such a problem cannot be solved by a simple combination of the above-mentioned related arts.
Moreover, any of the related arts assume the operation state between the time of initial installment of a device and the time of driving of the device. Therefore, in a case where an abnormality such as a blackout (i.e., major power outage) occurs, there is a problem of difficulty to realize the securement of operation flexibility and the maintenance of power input/output throughput by automatically executing fail-soft (i.e., degeneracy operation) and continuing power input/output.